One hallmark of the modern era of medicine has been the decline in morbidity and mortality associated with bacterial and fungal infections. However, misuse of conventional antibiotics and natural selection of the infectious bacterial population has resulted in the development of varying degrees of drug resistance by most bacterial infectious agents to most antibiotic agents. In severe cases, such as MRSA (Multidrug-Resistant StaphA), one or only a few antibiotics are currently effective. In addition, the existence of immunodeficiency syndromes results in additional incidence of opportunistic infections requiring intensive antibiotic treatment.
Thus, there continues to be a need in the medical arts for novel, more effective, antibiotic compounds, especially for treating bacterial infections, that are resistant to currently available therapies.
Boron containing compounds have received increasing attention as therapeutic agents over the past few years as technology in organic synthesis has expanded to include this atom. [Boron Therapeutics on the horizon, Groziak, M. P.; American Journal of Therapeutics (2001) 8, 321-328] The most notable boron containing therapeutic is the boronic acid bortezomib which was recently launched for the treatment of multiple myeloma. This breakthrough demonstrates the feasibility of using boron containing compounds as pharmaceutical agents. Boron containing compounds have been shown to have various biological activities including herbicides [Organic boron compounds as herbicides. Barnsley, G. E.; Eaton, J. K.; Airs, R. S.; (1957), DE 1016978 19571003], boron neutron capture therapy [Molecular Design and Synthesis of B-10 Carriers for Neutron Capture Therapy. Yamamoto, Y.; Pure Appl. Chem., (1991) 63, 423-426], serine protease inhibition [Borinic acid inhibitors as probes of the factors involved in binding at the active sites of subtilisin Carlsberg and α-chymotrypsin. Simpelkamp, J.; Jones, J. B.; Bioorganic & Medicinal Chemistry Letters, (1992), 2(11), 1391-4], [Design, Synthesis and Biological Evaluation of Selective Boron-containing Thrombin Inhibitors. Weinand, A.; Ehrhardt, C.; Metternich, R.; Tapparelli, C.; Bioorganic and Medicinal Chemistry, (1999), 7, 1295-1307], acetylcholinesterase inhibition [New, specific and reversible bifunctional alkylborinic acid inhibitor of acetylcholinesterase. Koehler, K. A.; Hess, G. P.; Biochemistry (1974), 13, 5345-50] and as antibacterial agents [Boron-Containing Antibacterial Agents: Effects on Growth and Morphology of Bacteria Under Various Culture Conditions. Bailey, P. J.; Cousins, G.; Snow, G. A.; and White, A. J.; Antimicrobial Agents and Chemotherapy, (1980), 17, 549-553]. The boron containing compounds with antibacterial activity can be sub-divided into two main classes, the diazaborinines, which have been known since the 1960's, and dithienylborinic acid complexes. This latter class has been expanded to include many different diarylborinic acid complexes with potent antibacterial activity [Preparation of diarylborinic acid esters as DNA methyl transferase inhibitors. Benkovic, S. J.; Shapiro, L.; Baker, S. J.; Wahnon, D. C.; Wall, M.; Shier, V. K.; Scott, C. P.; Baboval, J.; PCT Int. Appl. (2002), WO 2002044184]. Synthetic developments described in Benkovic et al. enabled creation of a much more diverse class of unsymmetrical di-substituted borinic acid complexes not possible before.